This invention relates to the construction of boats, specifically to the construction of lapstrake planked boat hulls.
Lapstrake planking is a traditional method of wooden boat building that has been in use for thousands of years. Like most wooden boats, lapstrake boats are built of planks, or strakes 1, which comprise the boat's hull. In lapstrake construction, each strake overlaps and is fastened to the outside face of the strake below. In other planking methods, the strakes are joined edge-to-edge.
Many boat builders favor the lapstrake method of building because it results in a boat that is less expensive and faster to build than one built with other traditional methods. Many boat owners also favor lapstrake construction for its aesthetic qualities, light weight, and lower construction costs. Lapstrake hulls are known to deflect water downward and thereby provide a "drier ride" then other hull types.
Lapstrake boat hulls are most often built over a strongback 2 and molds 3 as illustrated in FIG. 1A. The strongback is a frame to which molds that define the cross-sectional shape of the hull are attached. This structure forms the upside down shape of the hull. Individual strakes are shaped so as to cover the molds. Then the strakes nearest the keel are attached to the molds. A bevel 4, or angle, is cut in the edge of each strake and the next strake is attached to it using mechanical fasteners and/or glue as shown in FIG. 1B. The remaining strakes are attached in this manner until the hull is completed. Upon completion of planking, the hull is removed from the frame. Permanent frames, bulkheads, and other components may be incorporated into the molds and removed as part of the hull. Alternately, the frames, bulkheads or other components may be added to strengthen the hull after it is removed from the mold. There are several disadvantages to this method:
(a) It is time consuming and costly to construct a strongback 2 and molds 3 for each type of boat built; often, as much time is required to build the strongback and molds as to assemble the hull. PA1 (b) The shape of each strake 1 is determined by holding it against the molds. Each pair of planks, one for the port and one for the starboard side, are individually shaped and fit to the molds. This is a time consuming and exacting process demanding substantial skill on the builder's part. PA1 (c) A rolling, or constantly varying, bevel 4 must be cut in the edge of the strakes. This is time consuming and exacting, and it requires considerable skill of the builder. PA1 (a) It requires a boatbuilder possessing substantial skill, artistry, and experience, since the overall shape of the hull is largely determined by "eye" as it is being built, rather than by the molds. PA1 (b) A rolling, or constantly varying, bevel must be cut or planed into each strake in order to attach the next strake. This is time consuming and exacting, and it requires considerable skill of the builder. PA1 (c) The shape of each strake is determined by eye and fit to the boat without the molds to guide the builder. Each pair of planks, one for the port and one for the starboard side, are individually cut and fit without the aid of the molds. This is a time consuming process demanding substantial skill on the builder's part. PA1 (d) In practice, this method is limited as to the hull shapes that can be built. PA1 (a) The hull is not lapstrake construction that is favored by many boat builders for reasons of aesthetics as well as for reasons of functionality and economy. PA1 (b) This method demands extensive use of fiberglass and resins, which results in increased cost and increased environmental impact. PA1 (c) Fiberglass reinforced joints require additional sanding and finishing, particularly if the hull is to be finished with varnish or other clear coating, which many owners desire for aesthetic reasons. PA1 (a) It is difficult to hold such overlapped strakes in alignment since the forces of bending and twisting the strakes cause them to slip prior to being bonded. The plastic rivets must flex in order to accommodate the changes in angle between the strakes as the hull is assembled. This flexibility makes it difficult, if not impossible to precisely align the strakes. PA1 (b) Given the large number of strakes in some designs, the accumulated error caused by the changes, or errors, in the strakes' position may result in hull shapes substantially different than those the designer envisioned. PA1 (c) The rivets must be placed with great precision to assure the most accurate possible alignment of the strakes. PA1 (d) The lack of accuracy in strake alignment limits this method to boats with little bend in the strakes and does not allow designs containing substantial twist in the strakes-powerboats with both flare and tumblehome in the hulls, for example. PA1 (e) The amount of overlap between the strakes may not be consistent, which is detrimental to the aesthetics of the boat. PA1 (a) to provide a method where lapstrake boats are planked without need for a strongback and/or molds; PA1 (b) to provide a method of lapstrake construction where the cutting or planing of bevels on plank edges is not required; PA1 (c) to provide a simplified method of lapstrake construction heretofore the domain of skilled professional boat builders or students of boat building, thereby expanding the accessibility of such construction to home builders or builders with limited experience; PA1 (d) to provide a method of boat construction that is applicable to a wider range of hull shapes than current construction methods allow; PA1 (e) to provide a method of lapstrake construction where all the strakes can be cut and prepared prior to constructing the boat, thus speeding production time in that parts can be made and shipped from a production facility to home builders or regional boat shops. PA1 (f) to provide a method of lapstrake boat construction where all strakes may be cut on a numerical control router, thus lowering production cost and speeding production time for components; PA1 (g) to provide a method of lapstrake boatbuilding that allows assembly of the hull to be more economical than prior methods; PA1 (h) to provide a method of building where the boat may be completed in substantially less time than is possible with prior methods; PA1 (i) to provide a lapstrake joint with substantial surface area to allow a stronger glue joint and eliminate or reduce the need to reinforce joints with fiberglass reinforced plastics and/or epoxy fillets in boats built without strongbacks and forms; PA1 (j) To provide a lapstrake joint that aids in aligning the strakes as they are being joined and serves as an index to allow the builder to check that the strakes are properly overlapped and aligned; PA1 (k) To provide a method of boat building that requires less use of potentially unhealthy and environmentally harmful resins than many commonly used methods.
An alternate method of lapstrake planking is historically used in the Scandinavian countries. The hull is built without a strongback and molds. It is built right side up; the hull shape is established by placing posts under it and by using beams wedged against the ceiling of the workshop to form the strakes. Though this method eliminates the need to build a strongback and molds, it does have other disadvantages:
A more recent method illustrated in FIG. 2, termed "stitch-and-glue construction," also allows building boats without strongbacks and molds. The development of computer boat design programs has made it possible to easily determine the strake's exact shape, or expansion, and to cut the strakes prior to building the molds. Both the two-dimensional shape (that is, the shape when the strakes are cut from wood or other flat stock) and their three-dimensional shape (the shape after the strake is bent to form part of the hull) of the strakes can be calculated. Boats are now built without strongbacks and molds by butting the edges of the strakes and joining them with epoxy fillets 5 and fiberglass reinforced plastic 7. This technique has the following disadvantages:
A further refinement of the stitch-and-glue technique, illustrated in FIG. 4, involves overlapping the strakes 1 of a design to make a lapstrake boat. Flexible plastic rivets 6 are used to hold the strakes in position. The inventor knows of no articles or books describing this method as it has been developed in the past few years. This method has the following disadvantages: